The present technology relates to a thin film transistor having an organic semiconductor pattern, a method of manufacturing the same, and an electronic device using the thin film transistor.
In recent years, attention has been drawn to an organic thin film transistor which is a thin film transistor (hereinafter referred to as “TFTs”) including a channel layer made of an organic semiconductor material. All layers including the channel layer can be formed by coating or by printing so that a low-cost manufacturing can be achieved. Also, the channel layer can be formed at a lower temperature as compared to a method such as an evaporation method, so that the organic TFT can be mounted on a plastic film having a low heat resistance and flexibility.
The use of an organic TFT as a switching element for an electronic device such as a display device has been studied, as in an inorganic TFT including a channel layer made of an inorganic semiconductor material. The organic TFT includes: an organic semiconductor pattern which forms a channel layer; and source and drain electrodes connected to the organic semiconductor pattern.
When manufacturing the organic TFT, a process step is desired where an organic semiconductor layer is formed and the organic semiconductor layer is then selectively removed (patterned) to form an organic semiconductor pattern, in order to reduce an OFF state current. This process is, in general, called element isolation. In the process of manufacturing the organic TFT, unlike the process of manufacturing the inorganic TFT, the organic semiconductor pattern is readily dissolved in an organic solvent and there may be difficulties in performing the element isolation with the photolithography method that utilizes the organic solvent.
Several methods have been proposed for the element isolation. The methods are specifically described below. The YAG laser or the like is irradiated to a part of an organic semiconductor layer to sublimate unnecessary part (for example, see Japanese Patent Application Laid-Open Publication No. 2005-079225). A patterned insulating layer (such as silicon nitride) is formed on each of source and drain electrodes respectively, and then an organic semiconductor layer is formed. In this case, the organic semiconductor layer is isolated by utilizing a height difference (step difference) between a region where the patterned insulating layer is formed and a region where the patterned insulating layer is not formed (for example, see Japanese Patent Application Laid-Open Publication No. 2000-269504). A patterned layer (such as polyvinyl alcohol) is formed on an organic semiconductor layer and the organic semiconductor layer is then etched using the patterned layer as an etch mask (for example, see Japanese Patent Application Laid-Open Publication No. 2006-261312). An organic semiconductor layer and a gate insulating layer are formed in this order on source and drain electrodes and then both of the organic semiconductor layer and the gate insulating layer are patterned simultaneously using a laser ablation method (for example, see Japanese Patent No. 4137915). An organic semiconductor layer and a protection layer (such as silicon oxide) are formed in this order on source and drain electrodes and then both of the organic semiconductor layer and the protection layer are patterned simultaneously using the laser ablation method (for example, see Japanese Patent Application Laid-Open Publication No. 2006-332661). An organic semiconductor layer is formed on source and drain electrodes, and then a laser beam is irradiated onto regions other than the regions on which both the electrodes are not formed to pattern the organic semiconductor layer (for example, see Japanese Patent Application Laid-Open Publication No. 2008-524839 (Translation of PCT Application)). A protection layer (such as indium tin oxide (ITO)) and an organic semiconductor layer are formed in this order on source and drain electrodes, and then a laser beam is irradiated onto a region on which the protection layer is formed to pattern the organic semiconductor layer (for example, see Japanese Patent Application Laid-Open Publication No. 2007-165834).